A First Course in Quality Engineering, 2nd Edition

Quality in Production—Process Control II 327

previous observations weighted in an exponentially decreasing manner� By

choosing the value of λ appropriately, the relative importance given to the

most recent and past values can be changed� Larger values of λ will give

more importance to the most recent observation, and smaller values will

assign more importance to past values� The example below explains how the

EWMA chart is constructed and used�

Example 5.9

Table 5.8 has two sets of data. Column 2 has data from a normal process with mean

μ = 10 and σ = 1.0 up to Sample 20. The data after the 20th sample come from a

process with an average of 11.0, a change of one standard deviation (k = 1) in the

mean of the original process. Column 5 ...